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Friday,
31 January, 2003
100s of hominids have
been found at Sterkfontein. The fossil of an early human-like creature
(hominid) from southern Africa is raising fresh questions about our origins.
Remains from the Sterkfontein Caves near Johannesburg suggest our ancestors
were less chimp-like than we thought. The revelation follows the discovery
of missing bones from a 3.5 million-year-old skeleton found in 1998. This
Sterkfontein individual was a climber in the trees and bipedal on the
ground
Fragments of pelvis,
upper leg, ribs and backbone have recently been dug out of the rock, allowing
scientists to piece together its gait. The anatomy of the hominid, a member
of the genus Australopithecus, raises some interesting questions. Its
bone structure shows it did not walk like modern chimps, using the knuckles
of its hands.
It probably walked on two legs when it was on the ground but spent much
of the time climbing trees, says Dr Ron Clarke, of the University of the
Witwatersrand, who discovered the fossil.
Tool-making
Dr Clarke goes further. He argues that the fact the hominid was not a
knuckle-walker suggests chimps and humans are not as closely related as
we thought.
Knuckle-walking
and vertical climbing - up and down tree trunks - are a specialization
of chimps and gorillas after humans split off from them…Dr Robin
Crompton
It pushes the last common ancestor of chimps and humans much further back
in history, he says. Dr Clarke sets out his position in the South African
Journal of Science, which publishes the latest data. "My conclusion
from the limb proportions and the morphology of the foot and of the hand
is that this Sterkfontein individual was a climber in the trees (using
its powerful thumb in a vice-like grip) and bipedal on the ground,"
he says. "It would appear, therefore, that the strong opposable thumb
evolved in the human ancestral stock for grasping branches. Then, in the
mainly terrestrial subsequent descendants in the form of Homo, it was
to prove useful for tool-making and manipulation. "The suggestion
in reconstructions and in the scientific literature that human ancestors
were transformed into an upright position from a knuckle-walking ancestor
is not supported by this new and important addition to the fossil record."
Fresh debate
Other experts in human evolution are more circumspect. Professor Chris
Stringer of London's Natural History Museum says the idea that humans
and chimps derive from a knuckle- walking common ancestor is "not
a majority view".
The peculiar gait of chimps and gorillas could have developed after the
three lines diverged, he says. Dr Robin Crompton, of the University of
Liverpool, agrees. He says there is "very strong" genetic evidence
that we are closely related to chimps (and Bonobos). "It is likely
that the common ancestor of the African apes, including ourselves, was
arboreal," he told BBC News Online.
"In my view,
knuckle- walking and vertical climbing - up and down tree trunks - are
a specialization of chimps and gorillas after humans split off from them."
Sterkfontein is probably the richest site on Earth for the fossils of
early hominids, and the ancient cave system is now part of a World Heritage
Site. Some 600 hominid fossils from the Sterkfontein Caves have now been
collected and classified. The early humans they represent are thought
to have fallen to their deaths in the caves when the limestone complex
first broke the surface.
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